Oxidation of organic compounds

ABSTRACT

Volatile organic compounds are removed from contaminated soil, groundwater and the like by treatment with a combination of a water soluble peroxygen compound, such as a persulfate, and a pH modifier, such as sodium carbonate.

FIELD OF THE INVENTION

The present invention relates to the in situ and ex situ oxidation oforganic compounds in soils, groundwater, process water and wastewaterand especially relates to the in situ oxidation of volatile andsemi-volatile organic compounds, pesticides and herbicides, and otherrecalcitrant organic compounds in soil and groundwater.

BACKGROUND OF THE INVENTION

The presence of volatile organic compounds (VOCs), semi volatile organiccompounds (SVOCs) or pesticides in subsurface soils and groundwater is awell-documented and extensive problem in industrialized andindustrializing countries. Many VOC's and SVOC's are compounds which aretoxic or carcinogenic, are often capable of moving through the soilunder the influence of gravity and serving as a source of watercontamination by dissolution into water passing through the contaminatedsoil. These include, but are not limited to, chlorinated solvents suchas trichloroethylene (TCE), vinyl chloride, tetrachloroethylene (PCE),methylene chloride, 1,2-dichloroethane, 1,1,1-trichloroethane (TCA),carbon tetrachloride, chloroform, chlorobenzenes, benzene, toluene,xylene, ethyl benzene, ethylene dibromide, methyl tertiary butyl ether,polyaromatic hydrocarbons, polychlorobiphenyls, phthalates, 1,4-dioxane,nitrosodimethyl amine, and methyl tertbutyl ether.

In many cases discharge of these compounds into the soil leads tocontamination of aquifers resulting in potential public health impactsand degradation of groundwater resources for future use. Treatment andremediation of soils contaminated with VOC or SVOC compounds have beenexpensive, require considerable time, and in many cases incomplete orunsuccessful. Treatment and remediation of volatile organic compoundsthat are either partially or completely immiscible with water (i.e., NonAqueous Phase Liquids or NAPLs) have been particularly difficult. Alsotreatment of highly soluble but biologically stable organic contaminantssuch as MTBE and 1,4-dioxane are also quite difficult with conventionalremediation technologies. This is particularly true if these compoundsare not significantly naturally degraded, either chemically orbiologically, in soil environments. NAPLs present in the subsurface canbe toxic to humans and other organisms and can slowly release dissolvedaqueous or gas phase volatile organic compounds to the groundwaterresulting in long-term (i.e., decades or longer) sources of chemicalcontamination of the subsurface. In many cases subsurface groundwatercontaminant plumes may extend hundreds to thousands of feet from thesource of the chemicals resulting in extensive contamination of thesubsurface. These chemicals may then be transported into drinking watersources, lakes, rivers, and even basements of homes throughvolatilization from groundwater.

The U.S. Environmental Protection Agency (USEPA) has established maximumconcentration limits for various hazardous compounds. Very low andstringent drinking water limits have been placed on many halogenatedorganic compounds. For example, the maximum concentration limits forsolvents such as trichloroethylene, tetrachloroethylene, and carbontetrachloride have been established at 5 .mu.g/L, while the maximumconcentration limits for chlorobenzenes, polychlorinated biphenyls(PCBs), and ethylene dibromide have been established by the USEPA at 100.mu.g/L, 0.5 .mu./L, and 0.05 .mu.g/L, respectively. Meeting thesecleanup criteria is difficult, time consuming, costly, and oftenvirtually impossible using existing technologies.

The literature teaches the use of strong oxidizing agents to treatcontaminated soil by chemically degrading recalcitrant and hazardouschemicals, either in situ or ex situ. Such oxidizers include Fenton'sreagent, ozone, potassium permanganate and persulfates. One key aspectto the ability of an oxidizer to function is its ability to permeatethrough the subsurface, interacting with target compounds throughout theentire zone of contamination. Oxidizing species, such as peroxide, ozoneand hydroxyl radicals have relatively short lifetimes within thesubsurface. Persulfate radicals survive for greater periods. Howeverthere is a desire to have even longer lived active species available fororganic species decomposition in order to increase the zone or reaction,without resorting to multiple injection points throughout thecontamination area.

It is commonly known that the reactivity of hydrogen peroxide, throughthe production of hydroxyl radicals, requires acid conditions. Typicallyacid is added with the hydrogen peroxide to increase the rate ofreaction. Also, in many of its idustrial uses, persulfate solutions arealso kept under acidic conditions to increase their reactivity.

Persulfates have been shown to oxidize a wide range of recalcitrantchemicals, and in combination with either heat or catalyst, are highlyeffective. However, it is known that during the course of oxidation bypersulfate, the persulfate decomposition and reaction pathways generatesulfuric acid. One part of persulfate produces one part of sulfuricacid. If the buffering capacity of the nascent soil is not high enough,this acid production may yield a lowering of the ambient pH. While theacidic pH aids in the reactivity of the persulfate, low soil or ambientpH in the groundwater can be an issue, particularly resulting in themobilization of toxic metals in the subsurface, causing an increase inoxidant decomposition rates, or requiring further remediation to meetregulated pH guidelines.

SUMMARY OF THE INVENTION

The present invention relates to a method for the treatment ofcontaminated soil, sediment, clay, rock, and the like (hereinaftercollectively referred to as “soil”) containing volatile organiccompounds, semi-volatile organic compounds, pesticides and herbicides,as well as the treatment of contaminated groundwater (i.e., water foundunderground in cracks and spaces in soil, sand and rocks), process water(i.e., water resulting from various industrial processes) or wastewater(i.e., water containing domestic or industrial waste, often referred toas sewage) containing these compounds.

The method of the present invention uses one or more water solubleoxidants in combination with a pH modifier, where the pH modifiermaintains a pH in the range of 6-10, under conditions which enableoxidation of most, and preferably substantially all, the organiccompounds in the soil, groundwater, process water and/or wastewater,without the deleterious effects of metal mobilization or oxidantdecomposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the relationship between the mole ratio ofcarbonate to persulfate ions; catalyst level and pH

FIG. 2 is a graph showing pH as a function of the mole ratio ofcarbonate to persulfate ions.

FIG. 3 is a diagram showing the loss of persulfate as a function ofcatalyst and carbonate levels

FIG. 4 is a graph showing persulfate stability as a function of pH

FIG. 5 is a diagram showing residual VOC's as a function of carbonateand catalyst levels.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the process of the present invention, organiccompounds are oxidized by contacting the organic compound with acomposition comprising (a) a water soluble peroxygen compound and (b) apH modifier—i.e., any compound which is capable of stabilizing the pH,or buffering, the composition in its intended environment.

The oxidant may be any solid phase water soluble peroxygen compound,introduced into the soil or water in amounts, under conditions and in amanner which assures that the oxidizing compound is able to contact andoxidize most, and preferably substantially all, the target compounds.

In a preferred embodiment of the invention a composition comprisingsodium carbonate and a peroxygen compound is introduced into the soil insufficient quantities to satisfy the soil oxidant demand, compensate fordecomposition, and to oxidize the target compounds. The quantity thatneeds to be added to control the pH in thae range of 6 to 10 is lessthan the stoichiometric requirement. On a stoichiometric basis each partof persulfate used requires one part of sodium carbonate to neutralizethe acid produced. This equates to a mole ration of 1:1.

The use of carbonate to modify the pH of a peroxygen oxidant such aspersulfate is an unanticipated result. Carbonate is a known radicalscavenger and interferes with the ability of hydroxyl radicals tooxidize organics. (“Photocatalytic degradation of aqueous organicsolvents, in the presence of hydroxyl radical scavengers,” MehrabMehrvar, William A. Anderson, and Murray Moo-Young, InternationalJournal Of Photoenergy 2001; Chemical Models of Advanced OxidationProcesses, William H. Glaze, Fernando Beltran, Tuula Tuhkanen andJoon-Wun Kang, Water Pollution Research Journal of Canada, 27(1): 23-42(1992)). It would be expected that carbonate would also inhibit thereactivity of sulfate radicals.

This pH modification methodology may also be used ex situ to treatquantities of contaminated soil which have been removed from the ground.

According to another aspect of the present invention, under conditionswhere metal cations are present in the contaminated soil or water, thepersulfate and carbonate composition may be introduced into thecontaminated soil to remove the target compounds. The metal cationscatalytically decompose the persulfate to form sulfate free radicals,which oxidize the target VOCs. If the metal cations are not naturallypresent in sufficient quantities, they may be added from an externalsource. Such metal cations include divalent transition metals such asFe⁺². Also, chelated metal ions, such as Fe⁺³ chelated with EDTA, wherethe chelant provides enhanced stability and solubility of the metal ion,may be added.

As per another aspect of the present invention, the persulfate andcarbonate composition may be introduced into the soil, followed byheating of the soil to active the persulfate free radicals. Likewise,the persulfate and carbonate composition may be introduced into soilthat has already been pre-heated for activation of persulfate freeradicals.

In one embodiment of the present invention, the oxidation of organiccompounds at a contaminated site is accomplished by the injection of acombination of persulfate and a carbonate into the soil.

In a preferred form of the invention, sodium persulfate (Na.sub.2S.sub.2 O.sub.8) is introduced into the soil.

For in situ soil treatment, injection rates must be chosen based uponthe hydrogeologic conditions, that is, the ability of the oxidizingsolution to displace, mix and disperse with existing groundwater andmove through the soil. Additionally, injection rates must be sufficientto satisfy the soil oxidant demand and chemical oxidant demand in arealistic time frame and to compensate for any decomposition of theoxidant. It is advantageous to clear up sites in both a cost effectiveand timely manner. Careful evaluation of site parameters is crucial. Itis well known that soil permeability may change rapidly both as afunction of depth and lateral dimension. Therefore, injection welllocations are also site specific. Proper application of any remediationtechnology depends upon knowledge of the subsurface conditions, bothchemical and physical, and the present process is not different in thatrespect.

While sodium persulfate is the preferred peroxygen compound foroxidizing soil constituents, other solid phase water soluble peroxygencompounds can be used. By “solid phase water soluble peroxygen compound”it is meant a compound that is solid and water soluble at roomtemperature and contains a bi-atomic oxygen group, O—O. Such compoundsinclude all the dipersulfates, monopersulfates, peroxides, and the like,with the dipersulfates being preferred because they are inexpensive andsurvive for long periods in groundwater saturated soil under typicalsite conditions.

The most preferred dipersulfate is sodium persulfate as it has thegreatest solubility in water and is least expensive. Moreover, itgenerates sodium and sulfate upon reduction, both of which arerelatively benign from environmental and health perspectives. Potassiumpersulfate and ammonium persulfate are examples of other persulfateswhich might be used. Potassium persulfate, however, is an order ofmagnitude less soluble in water than sodium persulfate; and ammoniumpersulfate is even less desirable as it may decompose into constituentswhich are potential health concerns.

In addition to sodium carbonate, examples of other pH modifiers that maybe used include calcium carbonate, sodium bicarbonate, sodium andpotassium phosphate, potassium carbonate, potassium bicarbonate, sodiumsesquicarbonate, potassium sesquicarbonate, sodium borate, and TRISbuffer (Tris Hydroxymethylaminoethane). The weight ratio of persulfateto carbonate may be varied over a wide range depending upon the soilconditions and final target pH. A preferred ratio is 90 parts ofpersulfate and 10 parts of sodium carbonate which is less than thestoichiometric requirement for acid neutralization. It is also preferredto combine the persulfate and carbonate as a dry blend prior to shipmentto the site where the composition is to be used. Thus it is desirablethat the solid pH modifier be stable and non-hydroscopic. Thecarbonate/bicarbonate modifiers have such properties. However, it isalso possible to combine the two ingredients to prepare the compositionat the site. Alternatively, the persulfate and the pH modifier may beinjected sequentially at the site and the composition formed in situ.

The persulfate and pH modifier, being compatible with each other, may bemixed together and shipped or stored prior to being combined with waterin the same vessel prior to injection. It is preferred that enoughpersulfate is present to satisfy substantially all the soil oxidantdemand and to destroy the target compounds to acceptable levels, or asclose thereto as possible, and enough pH modifier is present to maintaina pH between 6 and 8.

Depending upon the type of soil, target compounds, and other oxidantdemand by the site, the concentrations of persulfate used in the presentinvention may vary from 0.5 g/L to greater than 250,000 mg/L. Thepreferred concentrations are a function of the soil characteristics,including the site-specific oxidant demands. Hydrogeologic conditionsgovern the rate of movement of the chemicals through the soil, and thoseconditions must be considered together with the soil chemistry tounderstand how best to perform the injection. The techniques for makingthese determinations and performing the injections are well known in theart. For example, wells or borings can be drilled at various locationsin and around the suspected contaminated site to determine, as closelyas possible, where the contamination is located. Core samples can bewithdrawn, being careful to protect the samples from atmosphericoxidation. The samples can then be used to determine soil oxidant demandand chemical (e.g. VOC) oxidant demand and the oxidant stabilityexisting in the subsurface. The precise chemical compounds in the soiland their concentration can be determined. Contaminated groundwater canbe collected. Oxidants can be added to the collected groundwater duringlaboratory treatability experiments to determine which compounds aredestroyed, in what order and to what degree, in the groundwater. It canthen be determined whether the same oxidants are able to destroy thosechemicals in the soil environment.

One method for calculating the preferred amount of peroxygen compound tobe used per unit soil mass (for an identified volume of soil at thesite) is to first determine the minimum amount of persulfate needed tofully satisfy soil oxidant demand per unit mass of uncontaminated soil.A contaminated soil sample from the identified volume of soil is thentreated with that predetermined (per unit mass) amount of persulfate;and the minimum amount of peroxygen compound required to eliminate theorganic compounds in that treated sample is then determined. Chemicalreaction stoichiometry governs the mass/mass ratios and thus the totalamount required to achieve the desired result. In actuality the amountof peroxygen compound injected into various locations at a singlecontaminated site will vary depending upon what is learned from the coresamples and other techniques for mapping what is believed to be thesubsurface conditions.

The goal is for the concentration of peroxygen compound in the injectedsolution to be just enough to result in the peroxygen compound reactionfront traveling throughout the area of contamination requiring treatmentin sufficient quantity to oxidize the contaminants present. (Thesaturated soil zone is the zone of soil which lies below the water tableand is fully saturated. This is the region in which groundwater existsand flows.) In certain saturated soil zones where the natural velocityof the groundwater is too slow for the purposes of treatment within acertain timeframe, the velocity of groundwater can be increased byincreasing the flow rate of the injected solution or installation ofgroundwater extraction wells to direct the flow of the injectedperoxygen compound solution. Certain soils to be treated may be inunsaturated zones and the method of peroxygen compound injection may bebased on infiltration or trickling of the peroxygen compound solutioninto the subsurface to provide sufficient contact of the soils with theinjected chemicals. Certain soils and conditions will require largeamounts of peroxygen compound to destroy soil oxidant demand, whileother soils and conditions might not. For example, sandy soils havinglarge grain size might have very little surface area, very littleoxidizable compounds and therefore very little soil oxidant demand. Onthe other hand, silty or clayey soils, which are very fine grained,would have large surface area per unit volume. They are likely to alsocontain larger amounts of oxidizable compounds and thus have a higheroverall soil oxidant demand.

The amount of pH modifier used in the present invention may vary fromthose having a mole ratio of carbonate ion to persulfate ion of fromgreater than 0.01 to less than 1.0 (the theoretical stoichiometricrequirement). Preferred results are achieved with a carbonate ion topersulfate ion mole ratio of from 0.10 to 0.30.

In addition to in situ applications the process may also be employed exsitu. In addition to soil it may be used to treat sludges, sands, tars,groundwater, wastewater, process water or industrial water.

Another exemplary form of the invention is useful for destroyingrelatively low level, but unacceptable, concentrations of organiccompounds in groundwater.

In order to describe the invention in more detail, the followingexamples are set forth:

EXAMPLE 1

Solid sodium persulfate, sodium carbonate and activator (Fe(II) orFe-EDTA) were added to 40 mL brown glass vials at the appropriate massesto obtain targeted concentrations

Distilled water was added to the vial to contain zero headspace and thevial was capped with a teflon lined silicon rubber screw top to preventvolatile loss

A mixture of the volatile organic compounds (in methanol) was injectedthrough the septum of the sealed vials into the water/oxidant/activatormixture.

Controls were constructed, without the addition of sodium persulfate,identical to the reaction vials

All vials were reacted at room temperature for 7 days.

Following 7 day reaction period, vials were stored at 4 deg C. foranalysis.

Analyses were performed on a gas chromatograph/mass spectrometerutilizing USEPA SW-846, Method 8260B

Reaction data were compared to control data in order to factor out anynon-oxidative (i.e., volatile) losses that may have occurred

The % reduction of organics results are shown in the following tablePercent Reduction Relative to Control Fe II, Fe-EDTA, Carbonate %reduction CO3 Fe II CO3 Fe-EDTA Only VC 100 100 0 1,1-DCE 100 100 100100 2.83 MTBE 93.9 85.4 45.9 50.7 0 n-Hexane 98.9 94.5 0 cis-DCE 99.5100 100 100 0 Chloroform 73.8 0 24.3 0 0 TCA 23.1 0 38.2 0 0 Benzene 100100 100 98.8 0 TCE 98.8 100 100 100 1.9 Toluene 100 100 100 100 0 PCE100 100 100 73.6 9.9 chlorobenzene 100 100 100 100 1.9 Methylene Cl 94.88.3 90.2 0 6.6 pH (Control 6.4) 9.9 2.2 8.5 2.3 11.2

It can be seen in this example that addition of carbonate to the samplemaintains a higher pH than those samples without the buffer, withoutreducing the overall efficacy of the persulfate. In a couple of cases,addition of carbonate actually enhance the decomposition of the targetorganic compound. This is unexpected as carbonate is known to be aradical scavenger and decreases the reactivity of hydroxyl radicals.

EXAMPLE 2

An experiment was conducted to determine the levels of buffer to add toa VOC containing solution being dosed with sodium persulfate. 40 mLbrown glass vials were dosed with a stock contaminate solutioncontaining the following compounds in methanol: chlorinated ethenes(tectrachloroehane, trichloroethene, cis-1,2-dichloroethene,1-1-dichloroethene, vinyl chloride), aromatics (benzene, toluene,chlorobeneze), chloroform, 1,1,1-trichloroethane, n-hexane, andmethyl-tert-butyl ether. To this solution was added 3.95 g of sodiumpersulfate, representing a two-fold stoichiometric dose for all of theorganics. Catalyst (Fe-EDTA) and sodium carbonate were added in varyingamounts. Analyses were performed on a gas chromatograph/massspectrometer utilizing USEPA SW-846, Method 8260B. Comparisons were madebetween untreated (no persulfate) levels of contaminant and treatedlevels.

In the trials where no buffer was added, the pH of the sample vials wereall below 2. FIG. 1 shows the relationship between measured pH afterseven days of reaction and the mole ratio between carbonate andpersulfate as well as catalyst (Fe-EDTA) level. From the figure, the7^(th) day pH is most strongly dependent upon the carbonate topersulfate ratio. A carbonate to persulfate ratio of 0.1 to 0.5 resultsin a pH range of 4.5 to 9.0. FIG. 2 displays the relationship of pH tomole ratio of carbonate to persulfate, removing the effects of thecatalyst level. As can be seen, there is a “breakpoint” in the pHresponse at a carbonate to persulfate mole ration of about 0.2. The pHmodification response holds true for catalyzed (Fe-EDTA) and uncatalyzedpersulfate.

The amount of persulfate remaining was determined after 3 and 7 days.Although the loss of persulfate due to either reaction with the VOC's orthrough non-productive decomposition was not distinguishable, acorrelation was determined between the average percent of VOC's removedand the amount of persulfate remaining. The correlation was 79% for thethree-day results and 74% for the seven-day results. This suggests thatthe greater the loss of persulfate the poorer the oxidation of theVOC's, indicating that minimizing the loss of persulfate throughdecomposition will improve the oxidative performance.

FIG. 3 shows the loss of persulfate after seven days as a function ofcatalyst (Fe-EDTA) loading and carbonate loading. From this figure itcan be seen that there is a strong correlation between catalyst loadingand persulfate loss (98% correlation). The effect of carbonate loadingwas dependent upon catalyst level. At catalyst levels below 150 mg/L Fe,the addition of carbonate had a general positive effect on persulfateloss. At high levels of catalyst loading (>300 mg/L Fe), reducing thelevel of carbonate, or going to high levels of carbonate werebeneficial, while intermediate amounts were generally worse. FIG. 4shows the effect of carbonate loading averaged over all trials where thecatalyst loading was 100 mg/L Fe or less. From the figure, it can beseen that below a carbonate to persulfate ratio of 0.2, the persulfatestability is degraded, and at ratios greater than 1.0, the stabilityalso begins to decrease. Thus the addition of carbonate at the properlevels will improve the persulfate stability.

EXAMPLE 3

This study was run essentially the same as Example 2. However thecontaminants were dispersed in water as compared to methanol, and thenumber of contaminants were increased. The contaminants included:tetrachloroethane, trichloroethene, cis-1,2-dichlorethene,trans-1,2-dichloroethene, 1,1-dichloroethene, 1-1-dichloroethane,1,2-dichlorethane, 1,1,1-trichloroethane, carbon tetrachloride,methylene chloride, chloroform, benzene, toluene, m,p,o-xylene,chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene,1,2,4-trichlorobenzene, 1,4-dioxane, tertbutyl alcohohol, MTBE and4-methyl-2-pentanone. Sodium persulfate was added to meet twice thestoichiometric demand of oxidizing all of the VOC's, and catalyst(Fe-EDTA) and sodium carbonate were added in varying amounts.

There was a 98% correlation between pH and carbonate to persulfate ratioafter seven days. The following table displays the resultant pH.Carbonate to 0 0.1 0.2 0.3 Persulfate ratio pH after 7 days 2.0 7.6 8.59.3

FIG. 5 shows the total residual VOC's after seven days of reaction time.The total initial VOC concentration was 329 mg/L. Optimal conditions for100 mg/L Fe catalyst result in a carbonate to persulfate ratio of0.15-0.20. For 300 mg/L Fe, the optimal carbonate to persulfate ratio is0.25-0.30. This demonstrates that the addition of carbonate to apersulfate solution allows less catalyst to be used. Reducing the amountof catalyst has several beefits. First it improves the stability of thepersulfate. Second it lowers the cost of the application.

1. A method for oxidizing an organic compound comprising contacting theorganic compound with a composition comprising a water soluble peroxygencompound and a pH modifier.
 2. A method as in claim 1, wherein theorganic compound is present in soil, groundwater, process water orwastewater.
 3. A method as in claim 1, wherein the organic compound isselected from the group consisting of volatile organic compounds,semi-volatile organic compounds, polyaromatic hydrocarbons,polychlorobiphenyls, pesticides and herbicides.
 4. The method as inclaim 1, wherein the peroxygen compound is a dipersulfate.
 5. The methodas in claim 4, wherein the dipersulfate is selected from sodium,potassium or ammonium persulfate or a combination thereof.
 6. The methodas in claim 1, wherein the peroxygen compound is a monopersulfate. 7.The method as in claim 6, wherein the monopersulfate is selected fromsodium and potassium monopersulfate.
 8. The method as in claim 1,wherein the peroxygen compound is a combination of a dipersulfate and amonopersulfate.
 9. The method as in claim 1 wherein the pH modifier issodium carbonate.
 10. The method as in claim 9 wherein carbonate andpersulfate are added in combination so that the mole ratio of carbonateion to persulfate ion is greater than 0.01 but less than 1.0.
 11. Themethod as in claim 10 wherein the carbonate and persulfate are added incombination so that the mole ratio of carbonate ion to persulfate ion isgreater than 0.10 but less than 0.30.
 12. The method as in claim 1wherein the pH modifier is sodium bicarbonate.
 13. The method as inclaim 1, wherein the composition is introduced into soil in sufficientquantities and under conditions to oxidize substantially all thevolatile organic compounds in the soil.
 14. The method as in claim 13,wherein the composition is introduced into the soil either in situ or exsitu.
 15. The method as in claim 14, wherein the soil is heated to atemperature up to 99 degrees C.
 16. A method for oxidizing organiccompounds comprising contacting the compounds with a compositioncomprising a water soluble peroxygen compound, a pH modifier, and acatalyst.
 17. A method as in claim 16, wherein the organic compound isselected from the group consisting of volatile organic compounds,semi-volatile organic compounds, polyaromatic hydrocarbons,polychlorobiphenyls, pesticides and herbicides.
 18. The method as inclaim 16, wherein the peroxygen compound is a dipersulfate.
 19. Themethod as in claim 18, wherein the dipersulfate is selected from sodium,potassium or ammonium persulfate or a combination thereof.
 20. Themethod as in claim 16, wherein the peroxygen compound is amonopersulfate.
 21. The method as in claim 20, wherein themonopersulfate is selected from sodium and potassium monopersulfate. 22.The method as in claim 16, wherein the peroxygen compound is acombination of a dipersulfate and a monopersulfate.
 23. The method as inclaim 16 wherein the pH modifier is sodium carbonate.
 24. The method asin claim 23 wherein carbonate and persulfate are added in combination sothat the mole ratio of carbonate ion to persulfate ion is greater than0.01 but less than 1.0.
 25. The method as in claim 24 wherein thecarbonate and persulfate are added in combination so that the mole ratioof carbonate ion to persulfate ion is greater than 0.10 but less than0.30.
 26. The method as in claim 16 wherein the pH modifier is sodiumbicarbonate.
 27. The method as in claim 16 wherein the catalyst consistsof a divalent or trivalent transition metal.
 28. The method as in claim16 wherein the catalyst consists of a divalent or trivalent transitionmetal in combination with a chelating agent.
 29. The method as in claim16, wherein the composition is introduced into soil in sufficientquantities and under conditions to oxidize substantially all thevolatile organic compounds in the soil.
 30. The method as in claim 28,wherein the composition is introduced into the soil either in situ or exsitu.
 31. The method as in claim 29, wherein the soil is heated to atemperature up to 99 degrees C.